problem with this program

Hey everyone, I'm in need of help to this matlab program I need to make. I've tried a for loop but i'm afraid i'm not doing something right. I need to write a program that accepts an input string from the user and determines how many times a user-specified character appears within the string. As an example, say I put in the word Mississippi, and want it to tell me how many s' are in there, capital and lowercase. Thanks for the help!